Manufacturing process for solid state lighting device on a conductive substrate

ABSTRACT

A method for fabricating a light emitting device includes forming a trench in a first surface on a first side of a substrate. The trench comprises a first sloped surface not parallel to the first surface, wherein the substrate has a second side opposite to the first side of the substrate. The method also includes forming light emission layers over the first trench surface and the first surface, wherein the light emission layer is configured to emit light and removing at least a portion of the substrate from the second side of the substrate to form a protrusion on the second side of the substrate to allow the light emission layer to emit light out of the protrusion on the second side of the substrate.

The present application is a Continuation-in-Part (CIP) application ofand claims priority to commonly assigned pending U.S. patent applicationSer. No. 12/691,269, entitled “Solid state lighting device on aconductive substrate”, filed Jan. 21, 2010, the content of which isincorporated herein by reference.

BACKGROUND

The present patent application is related to solid state light emissiondevices.

Solid-state light sources, such as light emitting diodes (LEDs) andlaser diodes, can offer significant advantages over incandescent orfluorescent lighting. The solid-state light sources are generally moreefficient and produce less heat than traditional incandescent orfluorescent lights. When LEDs or laser diodes are placed in arrays ofred, green and blue elements, they can act as a source for white lightor as a multi-colored display. Although solid-state lighting offerscertain advantages, conventional semiconductor structures and devicesused for solid-state lighting are relatively expensive. The high cost ofsolid-state light emission devices is partially related to therelatively complex and time-consuming manufacturing process forsolid-state light emission devices.

Referring to FIG. 1, a conventional LED structure 100 includes asubstrate 105, which may be formed of sapphire, silicon carbide, orspinel, for example. A buffer layer 110 is formed on the substrate 105.The buffer layer 110 serves primarily as a wetting layer, to promotesmooth, uniform coverage of the sapphire substrate. The buffer layer 310is typically deposited as a thin amorphous layer using Metal OrganicChemical Vapor Deposition (MOCVD). An n-doped Group III-V compound layer120 is formed on the buffer layer 110. The n-doped Group III-V compoundlayer 120 is typically made of GaN. An InGaN quantum-well layer 130 isformed on the n-doped Group III-V compound layer 120. An active GroupIII-V compound layer 140 is then formed on the InGaN quantum-well layer130. A p-doped Group III-V compound layer 150 is formed on the layer140. A p-electrode 160 (anode) is formed on the p-doped Group III-Vcompound layer 150. An n-electrode 170 (cathode) is formed on then-doped Group III-V compound layer 120.

A drawback in the conventional LED devices is that different thermalexpansions between the group III-V nitride layers and the substrate cancause cracking in the group III-V nitride layers or delamination betweenthe group III-V nitride layers from the substrate.

A factor contributing to complexity in some conventional manufacturingprocesses is that it requires a series of selective etch stages. Forexample, the cathode 170 in the conventional LED structure 100 shown inFIG. 1 is formed on the n-doped Group III-V compound layer 120 byselectively etching. These selective etch stages are complicated andtime-consuming and, therefore, make the overall manufacturing processmore expensive.

It is also desirable to increase active light emission intensities. Theconventional LED device in FIG. 1, for example, includes non-lightemission areas on the substrate 105 that are not covered by the InGaNquantum-well layer 130 to make room for the n-electrode 170. Thep-electrode 160 can also block some of the emitted light from leavingthe device. These design characteristics reduce the emission efficiencyof the conventional LED devices.

Another requirement for LED devices is to properly directinward-propagating light emission to the intended light illuminationdirections. A reflective layer is often constructed under the lightemission layers to reflect light emission. One challenge associated witha metallic reflective layer is that the metals such as Aluminum havelower melting temperatures than the processing temperatures fordepositing Group III-V compound layers on the metallic reflective layer.The metallic reflective layer often melts and loses reflectivity duringthe high temperature deposition of the Group III-V compound layers.

SUMMARY OF THE INVENTION

The disclosed light emitting device and associated manufacturingprocesses are intended to overcome above described drawbacks inconventional solid state lighting devices. Embodiments may include oneor more of the following advantages. An advantage associated with thedisclosed solid-state lighting structures and fabrication processes isthat active light emitting areas and light emission efficiency can besignificantly improved.

Another significant advantage associated with the disclosed solid-statelighting structures and fabrication processes is that a reflective layercan be properly formed under the light emission layers to effectivelyreflect the emitted light to intended light illumination directions.

Yet another significant advantage associated with the disclosedsolid-state lighting structures and fabrication processes is thateffective cooling can be provided by an entire conductive substrateduring the lighting operation.

Moreover, the electrodes are arranged on the opposite sides of thedisclosed light emission devices. Effective packaging techniques areprovided without using wire bonding, which makes the packaged lightemission modules more reliable and less likely to be damaged.Additionally, more than one light emission structure can be convenientlypackaged in a single light emission module, which reduces packagingcomplexity and costs.

Furthermore, the disclosed LED structures and fabrication processes canovercome lattice mismatch between the group III-V layer and thesubstrate, and can prevent associated layer cracking and delaminationthat are found in some conventional LED structures.

In one general aspect, the present invention relates to a method forfabricating a light emitting device. The method includes forming atrench or a truncated trench in a first surface on a first side of asubstrate, wherein the trench or a truncated trench comprises a firstsloped surface not parallel to the first surface, wherein the substratehas a second side opposite to the first side of the substrate; forminglight emission layers over the first trench surface and the firstsurface, wherein the light emission layer can emit light; and removingat least a portion of the substrate from the second side of thesubstrate to expose at least one of the light emission layers.

Implementations of the system may include one or more of the following.The method can further include forming a base electrode layer over thelight emission layers before the step of removing at least a portion ofthe substrate from the second side of the substrate, wherein the baseelectrode layer at least partially fills the trench or a truncatedtrench on the first side of the substrate. The base electrode layer canbe formed by electroplating or deposition over the light emission layerson the first side of the substrate. The base electrode layer can includea metallic material or a conducting polymer. The method can furtherinclude a reflective layer on the light emission layers, wherein thebase electrode layer is formed on the reflective layer. The method canfurther include forming a transparent conductive layer over the lightemission layers on the second side of the substrate after the step ofremoving at least a portion of the substrate from the second side of thesubstrate. The light emission layers can emit light in response to anelectric current flowing across the base electrode layer and thetransparent conductive layer. The substrate can include silicon, SiC,ZnO, Sapphire, or GaN. The first surface can be substantially parallelto a (100) crystal plane of the substrate, and wherein the first slopedsurface is substantially parallel to a (111) crystal plane of thesubstrate. The substrate can have a (100) crystal plane and a (111)crystal plane, wherein the first surface is substantially parallel tothe (111) crystal plane, and wherein the first sloped surface issubstantially parallel to the (100) crystal plane. The light emissionlayers can include at least one quantum well formed by Group III-Vcompounds. The quantum well can include: a first III-V nitride layer; aquantum-well layer on the first III-V nitride layer; and a second III-Vnitride layer on the quantum well layer. The method can further includeforming a buffer layer on the first sloped surface before the step offorming light emission layers, wherein the light emission layers areformed on the buffer layer. The buffer layer can include a materialselected from the group consisting of GaN, ZnO, AlN, HfN, AlAs, SiCN,TaN, and SiC. The step of removing can form a protrusion on the secondside of the substrate. The protrusion can have the shape of a pyramid ora truncated pyramid, wherein the first sloped surface is a substantiallyflat face in part defining the pyramid or the truncated pyramid.

In another general aspect, the present invention relates to a method forfabricating a light emitting device. The method includes forming lightemission layers having monolithic crystal structures on a siliconsubstrate, wherein the light emission layers can emit light when anelectric current flows across the light emission layers, wherein thesilicon substrate is on a first side of the light emission layers;forming abuse electrode layer over a second side of the light emissionlayers, the second side being opposite to the first side, wherein thebase electrode layer comprises anon-crystalline conductive material; andremoving at least a portion of silicon on the first side of the lightemission layers to expose at least one of the light emission layers. Thelight emission layers can include a monolithic quantum well formed byGroup III-V compounds. The non-crystalline conductive material caninclude a metallic material or a conducting polymer.

The method can further include a reflective layer on the first side ofthe light emission layers, wherein the base electrode layer is formed onthe reflective layer; and forming a transparent conductive layer overthe second side of the light emission layers after the step of removingat least a portion of the silicon substrate.

In another general aspect, the present invention relates to a method formaking a light emission module. The method can include constructing oneor more light emitting structures on a conductive substrate, whereineach of the one or more light emitting structures comprises lightemission layers and a transparent conductive layer on the light emissionlayers; attaching the one or more light emitting structures to amounting substrate by an electric interconnect, the mounting substratehaving a first electrode and a second electrode; allowing the firstelectrode to be in electrical connection with the conductive substrate;and allowing the second electrode to be in electric connection with thetransparent conductive layer, wherein the light emission layers in eachof one or more light emitting structures can emit light when an electriccurrent flows across the first electrode and the second electrode.

In another general aspect, the present invention relates to a lightemitting device that includes a conductive substrate having a firstsubstrate surface, wherein the conductive substrate includes aconductive material; a protrusion formed on the conductive substrate,wherein the protrusion can be defined in part by a first protrusionsurface that is not parallel to the first substrate surface; and lightemission layers disposed over the first protrusion surface, wherein thelight emission layers can emit light when an electric field is appliedacross the light emission layers.

Implementations of the system may include one or more of the following.The conductive material can include a metallic material or a conductingpolymer. The protrusion can have the shape of a pyramid or a truncatedpyramid, wherein the first substrate surface is a substantially flatface in part defining the pyramid or the truncated pyramid. The firstprotrusion surface can have an angle between 20 degrees and 80 degreesrelative to the first substrate surface. The light emission layers caninclude at least one quantum well formed by Group III-V compounds. Thequantum well can be formed by a first III-V nitride layer; aquantum-well layer on the first III-V nitride layer; and a second III-Vnitride layer on the quantum well layer. The light emitting device canfurther include a reflective layer formed between the conductivesubstrate and the light emission layers. The reflective layer caninclude aluminum, silver, gold, mercury, or chromium. The light emittingdevice can further include a transparent conductive layer formed overthe light emission layers, wherein the electric field across the lightemission layers is produced by a voltage applied between the transparentconductive layer and the conductive substrate. The light emitting devicecan further include an electrode layer around the protrusion, whereinthe electrode layer is in electric connection with the transparentconductive layer.

In another general aspect, the present invention relates to a lightemitting device that includes a non-crystalline conductive substrate;and light emission layers having monolithic crystal structures disposedover the conductive substrate, wherein the light emission layers canemit light when an electric field is applied across the light emissionlayers.

Implementations of the system may include one or more of the following.The light emission layers can include at least one monolithic quantumwell formed by Group III-V compounds. The monolithic quantum well can beformed by a first nitride layer; a quantum-well layer on the first III-Vnitride layer; and a second III-V nitride layer on the quantum welllayer. The light emitting device can further include a reflective layerformed between the conductive substrate and the light emission layers.The light emitting device can further include a transparent conductivelayer formed over the light emission layers, wherein the electric fieldacross the light emission layers is produced by a voltage appliedbetween the transparent conductive layer and the conductive substrate.The light emitting device can further include a protrusion formed on theconductive substrate, wherein the conductive substrate comprises a firstsubstrate surface outside of the protrusion, wherein the protrusion isdefined in part by a first protrusion surface that is not parallel tothe first substrate surface. The protrusion can have the shape of apyramid or a truncated pyramid. The non-crystalline conductive substratecan include a metallic material or a conducting polymer

In another general aspect, the present invention relates to a lightemission module that includes a mounting substrate having a firstelectrode and a second electrode; one or more light emitting structuresconstructed on a conductive substrate, wherein each of the one or morelight emitting structures comprises light emission layers and atransparent conductive layer on the light emission layers, wherein thelight emission layers in each of one or more light emitting structurescan emit light when a voltage is applied between the transparentconductive layer and the conductive substrate; and an electricinterconnect that can attach or clamp the one or more light emittingstructures to the mounting substrate to allow the first electrode to bein electrical connection with the conductive substrate and the secondelectrode to be in electric connection with the transparent conductivelayer.

Implementations of the system may include one or more of the following.The one or more light emitting structures can include one or moreprotrusions on the conductive substrate, wherein the light emissionlayers are formed on the one or more protrusions. The one or more lightemitting structures can further include an electrode layer around theprotrusion, the electrode layer in electric connection with thetransparent conductive layer, wherein the electric interconnect canelectrically connect the electrode layer to the second electrode. Theelectric interconnect can include a window over the light emissionlayers in the one or more light emitting structures to allow lightemitted from the light emission layers to pass through when the electricinterconnect clamps the one or more light emitting structures to themounting substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings, which are incorporated in and from a part of thespecification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view of a conventional LED structure.

FIG. 2 is a flowchart for fabricating the light emission devices inaccordance with an aspect of the present invention.

FIGS. 3A-3S are cross-sectional and perspective views illustrating thelight emitting structures at different steps in the flowchart in FIG. 2for fabricating the light emission device.

FIG. 4A is a detailed cross-sectional view illustrating a light emissionstructure with small lateral dimensions.

FIG. 4B is a detailed cross-sectional view illustrating a light emissionstructure with a flat conductive surface.

FIG. 5A shows the packaging of the light emission devices into lightemitting modules.

FIG. 5B shows the packaged light emission devices from FIG. 5A,

FIG. 6 is a flowchart for fabricating the light emission devices inaccordance with another aspect of the present invention.

FIGS. 7A-7J are cross-sectional views illustrating the light emittingstructures at different steps in the flowchart in FIG. 6 for fabricatingthe light emission device.

FIG. 8A shows the packaging of the light emission devices into lightemitting modules.

FIG. 8B shows the packaged light emission devices from FIG. 8A,

FIG. 9 is a schematic diagram illustrating angular distribution of lightemission from the light emitting device in accordance with the presentinvention.

DESCRIPTION OF THE INVENTION

Referring to FIGS. 2 and 3A-3D (FIGS. 3A and 3B are cross-sectionalviews along the A-A direction in FIG. 3C), a silicon substrate 300 has afirst side 310 and a second side 320 opposing to the first side 310. Thesilicon substrate 300 can for example be about 750 μm in thickness. Thesilicon substrate 300 includes a surface 301 on the first side 310. Thesubstrate 300 can be a (100) silicon wafer, that is the surface 301 isalong a (100) crystalline plane. A mask layer 302 is formed andpatterned on the surface 301. The mask layer 302 can be formed by asilicon nitride layer, or a silicon oxide layer. The mask layer 302 hasan opening 305 that exposes the silicon substrate 300 on the first side310. The silicon substrate 300 is then etched through the opening 305 toform a trench 308 (step 210). The trench 308 has a plurality ofsubstantially flat surfaces 331 that are not parallel or be slopedrelative to the surface 301. The surfaces 331 can form a reversepyramid, truncated trench, or a truncated reverse pyramid having asurface 332 that is substantially parallel to the surface 301. If thesubstrate 300 is a (100) silicon wafer, the surfaces 331 are (111)silicon surfaces and the surface 332 is a (100) silicon surface. Thesurfaces 331 are at a 54.7° angle relative to the surface 301 and thesurface 332. The mask layer 302 is then removed, leaving a trench havingsloped surfaces 331 in the substrate 300 on the first side 310 of thesubstrate 300 (step 215, FIG. 3D).

Referring to FIGS. 2, 3E and 3F, one or more buffer layers 335 are nextformed on the surface 301 and surfaces 331 (step 220). The bufferlayer(s) 335 can for example comprise AlN in a thickness range betweenabout 1 nm and about 1000 nm, such as 10 to 100 Angstroms. The bufferlayer(s) can include a thinner AlN layer (e.g. about 30 nm) formed onthe substrate 300 at a lower substrate temperature (e.g. 700° C.)followed by a deposition of a thicker AlN layer (e.g. about 70 nm)formed on the first thinner AlN layer at a higher substrate temperature(e.g. 1,200° C.). The buffer layer(s) 335 can also be formed of GaN,ZnO, HfN, AlAs, TaN, or SiC.

A plurality of light emitting layers 340 are next formed on the bufferlayer 335 (step 225). The light emitting layers 340 includesemiconductor quantum well layers that can produce and confine electronsand holes under an electric field. The recombination of the electronsand the holes can produce light emission. The emission wavelengths aredetermined mostly by the bandgap of the material in the quantum-welllayers. Exemplified light emitting layers 340 can include, from thebuffer layer 335 and up, an AlGaN layer (about 4,000 A in thickness), aGaN:Si layer (about 1.5 μm in thickness), an InGaN layer (about 50 A inthickness), a GaN:Si layer (about 100 A in thickness), an AlGaN:Mg layer(about 100 A in thickness), and GaN:Mg (about 3,000 A in thickness). TheGaN:Si layer (about 100 A in thickness) and the InGaN layer can berepeated several times (e.g. 3 to 7 times) on top of each other to forma periodic quantum well structure.

The buffer layer 335 and the light emitting layers 340 can be formedusing atomic layer deposition (ALD), Metal Organic Chemical VaporDeposition (MOCVD), Plasma Enhanced Chemical Vapor Deposition (PECVD),Chemical Vapor Deposition (CVD), or Physical vapor deposition (PVD). Theformation of the buffer layer(s) 335 between the substrate 300 and thelight emitting layers 340 can reduce mechanical strain between the (111)silicon surfaces of the substrate 300 and the light emitting layers 340,and prevent cracking and delamination in the light emitting layers 340.As a result, the quantum-well layers can have monolithic crystalstructures with matched crystal lattices. Light emitting efficiency ofthe LED device can be improved. Details of forming trenches, the bufferlayer, and the light emitting layers are disclosed in patent applicationSer. No. 12/177,114, titled “Light Emitting Device” filed on Jul. 21,2008 and patent application Ser. No. 11/761,446, titled “Silicon BasedSolid State Lighting” filed on Jun. 12, 2007 both by the presentinventor, the disclosures of which are incorporated herein by reference.

A reflective layer 345 is next, referring to FIGS. 2 and 3G, formed onthe light emitting layers 340 (step 230). The reflective layer 345 canbe formed by a layer of Aluminum approximately 500 nm in thickness. Thereflective layer 345 can also include materials such as Ag, Au, Hg, orCr.

A base electrode layer 350 is next formed on the reflective layer (FIG.3H, step 235). The base electrode layer 350 can include a metallicmaterial such as copper, aluminum, nickel, and iron, and can be formedby electroplating. The base electrode layer 350 can also include aconductive polymer material, which can be formed by coating. The baseelectrode layer 350 can have a layer thickness about 200 μm. Asdescribed below, the base electrode layer 350 can be used as one of theelectrodes for applying electric field across the light emitting layers340 and for cooling the light emitting device during operation. The baseelectrode layer 350 can fill at least a portion of the trench 308, whichcan leave a dimple 355, as shown in FIGS. 3H-3J. A plurality of trenches308 and related light emission layers 340 can be simultaneously formedon a single substrate (300) such as a silicon wafer, as shown in FIG.3J.

Next, the silicon material in the substrate 300 is removed from thesecond side 320 below the buffer layer 335 and the light emitting layers340 to expose the buffer layer 335 (FIG. 3K, step 240). As shown in abottom perspective view of FIG. 3L, the buffer layer 335 and the lightemitting layers 340 are thus disposed on the pyramids 360 on the secondside 320 of the substrate 300 (not shown in FIG. 3L because the siliconmaterial in the substrate 300 has been removed). As a result, a lightemitting structure 370 is partially formed. The light emitting structure370 is also shown in a top perspective view in FIG. 3M and in across-sectional view in FIG. 3N with the first side 310 and the secondside 320 are reversed in position (the reflective layer 345 is not shownin FIGS. 3L and 3M due to drawing scale).

Next, the buffer layer(s) 335 are removed from the second side 320 ofthe light emitting structure 370 (FIG. 3O, step 245). The light emittinglayers 340 are exposed to the second side 320. A transparent conductivelayer 375 comprising for example indium tin oxide (ITO) is next formedon the light emitting layers on the second side of the substrate (FIG.3P, step 250). The removal of the buffer layer(s) 335 allows thetransparent conductive layer 375 to be in contact with the lightemitting layers 340 to allow a voltage to be applied across the lightemitting layers 340.

A conductive ring layer (ring electrode) 380 is next formed on thetransparent conductive layer 375 around the pyramids as shown in FIGS.3Q-3S (step 255). (The light emitting layer 340 and the reflective layer345 in FIG. 3R are not shown due to drawing scale). The ring electrode380 can be formed by the same material (e.g. copper) as the baseelectrode layer 350 or Al. A notable feature of the light emittingstructure 370 is that the quantum-well layers having monolithic crystalstructures are formed over a non-crystalline conductive substrate thatare made of metals or conductive polymers. The monolithic crystalstructure of the quantum well layers allows the light emission layers340 that comprise the monolithic quantum layers to have high lightemission efficiency. The non-crystalline conductive substrate functionsas one of the two electrodes for applying the electric field, and canprovide cooling to the light emission device during operation.

It should be understood that the shape and the size the dimple 355 mayvary with the dimension of the light emission structure 370. A lightemission structure having a lateral dimension of 2 mm or larger may havea large and deep dimple 355 in the base electrode layer 350 as shown inFIG. 3H. A light emission structure 370 having a lateral dimensionsmaller than 2 mm may have a large and deep dimple 355 in the baseelectrode layer 350 as shown in FIG. 4A. Furthermore, as shown in FIG.4B, the base electrode layer 350 can be flattened on the first side 310by for example chemical mechanical polishing a flat conductive surface.The base electrode layer 350 can thus have a substantially flat surface390 on the first side 310 opposing to the light emission side (thesecond side 320) of the base electrode layer 350.

FIG. 5A shows an exploded view light emission modules 500 and 550, andthe packaging of light emission structures 370 into light emittingmodules 500 and 550 (step 260 in FIG. 2). An insulating substrate 400includes on its upper surface electrode layers 410, 420, 430. Theinsulating substrate 400 can be made of an insulating ceramic material,which can act as a heat sink. The light emission structure 370 includesa pyramid 360 on the base electrode layer 350. A plurality of lightemission layers (not shown) are formed on the pyramid 360. Thetransparent conductive layer 375 is formed on the light emission layers.The ring electrode 380 is formed around the pyramid 360 and in contactwith the transparent conductive layer 375. The light emission structure370 can be mounted directly on the electrode layer 420 on the insulatingsubstrate 400 such that the electrode layer 420 is in electric contactwith the base electrode layer 350. An electric interconnect 450 includesa window frame 451 having an opening therein and connected with two arms460 and 470. The electric interconnect 450 is made of an electricallyconductive material such as copper. The electric interconnect 450 can beclamped down such that the window frame 451 is in electric contact withthe ring electrode 380. The two arms 460 and 470 become respectively incontact with the electrode layers 410 and 430.

When the electric interconnect 450 and the light emission structure 370are tightly clamped to the substrate 400, the electrode layers 410 and430 are connected with the transparent conductive layer 375. Theelectrode layer 420 is connected with the base electrode layer 350. Anelectric voltage applied across the electrode layer 420 and theelectrode layers 410 and 430 can thus produce an electric field acrossthe light emission layers 340 (in FIGS. 3Q and 4, not shown in FIG. 5A),which can cause light emission in the light emission module 500 (shownin FIG. 5B).

In some embodiments, referring to FIGS. 6 and 7A-7J, a silicon substrate700 has a first side 710 having a surface 701 and a second side 720opposing to the first side 710. The substrate 700 can be a (100) siliconwafer with the surface 701 is along a (100) crystalline plane. Thesubstrate 700 can also be formed by SiC, Sapphire, or GaN. SiN layersare deposited on both the first side and the second side of the siliconsubstrate 700 (step 605, FIG. 7A). A mask layer 702M is formed bypatterning and selecting etching the SiN layer 702 on the surface 701(step 610, FIG. 7B). The mask layer 702M has an opening 705 that exposesthe silicon substrate 700 on the first side 710.

The silicon substrate 700 is then etched through the opening 705 to forma trench 708 (step 615, FIG. 7C). The trench 708 has a plurality ofsubstantially flat surfaces 731 that are not parallel or be slopedrelative to the surface 701. The surfaces 731 can form a reversepyramid. If the substrate 700 is a (100) silicon wafer, the surfaces 731are (111) silicon surfaces. The surfaces 731 are at a 54.7° anglerelative to the surface 701. Optionally, the mask layer 702M can then beremoved, leaving a trench having sloped surfaces 731 in the substrate700 on the first side 710 of the substrate 700.

One or more buffer layers (not shown for clarity) are next formed on thesurface 701, and surfaces 731 or the remaining hard mask layer 702M(step 620). The buffer layer(s) can comprise AlN in a thickness rangebetween about 1 nm and about 1000 nm, such as 10 to 100 Angstroms. Thebuffer layer and the light emitting layers 740 can be formed usingatomic layer deposition (ALD), Metal Organic Chemical Vapor Deposition(MOCVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), ChemicalVapor Deposition (CVD), or Physical Vapor Deposition (PVD).

A plurality of light emitting layers 740 are next formed on the bufferlayer (step 625, FIG. 7D). The light emitting layers 740 includesemiconductor quantum well layers that can produce and confine electronsand holes under an electric field. The recombination of the electronsand the holes can produce light emission. The emission wavelengths aredetermined mostly by the bandgap of the material in the quantum-welllayers. Exemplified light emitting layers 740 can include, from thebuffer layer, an AlGaN layer (about 4,000 A in thickness), a GaN:Silayer (about 1.5 μm in thickness), an InGaN layer (about 50 A inthickness), a GaN:Si layer (about 100 A in thickness), an AlGaN:Mg layer(about 100 A in thickness), and GaN:Mg (about 3,000 A in thickness). TheGaN:Si layer (about 100 A in thickness) and the InGaN layer can berepeated several times (e.g. 3 to 7 times) on top of each other to forma periodic quantum well structure. The light emitting layers 740 can forexample be formed by MOCVD.

The formation of the buffer layer(s) between the substrate 700 and thelight emitting layers 740 can reduce mechanical strain between the (111)silicon surfaces of the substrate 700 and the light emitting layers 740,and prevent cracking and delamination in the light emitting layers 740.As a result, the quantum-well layers can have monolithic crystalstructures with matched crystal lattices. Light emitting efficiency ofthe LED device can be improved. Details of forming trenches, the bufferlayer, and the light emitting layers are disclosed in patent applicationSer. No. 12/177,114, titled “Light Emitting Device” filed on Jul. 21,2008 and patent application Ser. No. 11/761,446, titled “Silicon BasedSolid State Lighting” filed on Jun. 12, 2007 both by the presentinventor, the disclosures of which are incorporated herein by reference.

After MOCVD layers, a surface treatment on top of GaN:Mg (about 3,000 Ain thickness) can be applied to further enhance light emittingefficiency. This treatment can be dry or wet etch with or withoutpatterning.

A reflective layer 745 is next formed on the light emitting layers 740(step 630, FIG. 7E). The reflective layer 745 can be formed by a layerof Aluminum approximately 500 nm in thickness. The reflective layer 345can also include materials such as Ag, Au, or Cr. The reflective layer345 can be formed by MOCVD, Electroplating, or PVD.

A base electrode layer 750 is next formed on the reflective layer (FIG.7F, step 635). The base electrode layer 750 can include a metallicmaterial such as copper, nickel, aluminum, chromium, and steel, and canbe formed by electroplating. The base electrode layer 750 can also beformed by a deposition method such as PVD, MBE, CVD, and PECVD. The baseelectrode layer 750 can also include a conductive polymer material,which can be formed by coating. The base electrode layer 750 can have alayer thickness from 50 to 500 μm. The base electrode layer 750 can beused as one of the electrodes for applying electric field across thelight emitting layers 740 and for cooling the light emitting deviceduring operation. The base electrode layer 750 can fill at least aportion of the trench 708, which can leave a dimple 755.

Next, the silicon material in the substrate 700 and the SiN layer 702are removed from the second side 720 below the buffer layer and thelight emitting layers 740 (FIG. 7G, step 640) (the device structure isflipped upside down from FIG. 7F to FIG. 7G). The light emitting layers740 are thus disposed on the pyramids 760 on the second side 720 of thesubstrate 700. As a result, a light emitting structure 770 is partiallyformed. The buffer layer (not shown for clarity) is removed from thesecond side 720 of the light emitting structure 770 (step 645) to exposethe light emitting layers 740 the second side 720 (FIG. 7G).

A transparent conductive layer 775 comprising for example ITO is nextformed on the light emitting layers on the second side of the substrate(FIG. 7H, step 650). The transparent conductive layer 775 is in contactwith the light emitting layers 740 to allow a voltage to be appliedacross the light emitting layers 740.

A conductive ring layer (ring electrode) 780 is next formed on thetransparent conductive layer 775 around the pyramids (FIG. 7I, step655). The ring electrode 780 can be formed by the same material (e.g.copper) as the base electrode layer 750 or Al. The light emittingstructure 770 is then diced to its final form. (FIG. 7J, step 660)

A notable feature of the light emitting structure 770 is that multiplepyramids 760 can be formed on a single device in a series of commonprocessing steps. The light emitting layers formed on the multiplepyramids can significantly increase lighting intensity. The number ofpyramids in a single light emitting structure can be varied to customizethe dimensions of the lighting device.

Another notable feature of the light emitting structure 770 is that thequantum-well layers having monolithic crystal structures are formed overa non-crystalline conductive substrate that are made of metals orconductive polymers. The monolithic crystal structure of the quantumwell layers allows the light emission layers that comprise themonolithic quantum layers to have high light emission efficiency. Thenon-crystalline conductive substrate functions as one of the twoelectrodes for applying the electric field, and can provide cooling tothe light emission device during operation.

Referring to FIGS. 8A and 8B, a light emission structure 470 includes aplurality of pyramids 360 formed on a common base electrode layer 350,as described above. A plurality of light emission layers (not shown dueto drawing scale) are formed on the pyramids 360. The transparentconductive layer 375 is formed on the light emission layers. A commonring electrode 380 is formed around the pyramids 360 and in contact withthe transparent conductive layer 375.

When the electric interconnect 450 and the light emission structure 470are tightly clamped to the substrate 400, the electrode layers 410 and430 are connected with the transparent conductive layer 375. Theelectrode layer 420 is connected with the base electrode layer 350. Anelectric voltage applied across the electrode layer 420 and theelectrode layers 410 and 430 can thus produce an electric field acrossthe light emission layers 340 (in FIGS. 3Q and 4, not shown in FIG. 8A),which can cause light emission in the light emission module 550 (FIG.8B).

An advantage of the light emission modules 500 and 550 is that there isno need for wire bonding to electrically connect the light emissionstructures 370 to external electrodes (410-430). As it is known thatwire bonding is easily damaged in the handling, the disclosed lightemission modules are thus more reliable than some conventionalsolid-state light emitting devices.

The packaging of light emitting modules (step 260 in FIG. 2) can alsoinclude dicing of light emitting structures on a substrate into dieseach containing smaller number of light emitting structures. Forexample, the light emitting structures 370 on the conductive substrate350 in FIG. 4B can be diced into dies each containing one or a few lightemitting structures which can subsequently form a light emitting moduleas shown in FIGS. 5A and 5B.

FIG. 9 is a schematic diagram illustrating angular distribution of lightemission from the light emitting device in accordance with the presentinvention. A light emitting device 370 includes a pyramid 360 formed ona base electrode layer 350. Light emitting layers having light emissionsurfaces 910, 920 are formed on the sloped surfaces of the pyramid 360.If the light emission structure 370 is formed with a (100) siliconwafer, the upper surface 930 is along the (100) crystalline plane andthe light emission surfaces 910, 920 parallel to the (111) crystallineplanes. The light emission surfaces 910, 920 are at a 54.7° anglerelative to the upper surface 930. For the same foot print on the uppersurface, the sum of the areas of the emission surfaces on the lightemission surfaces 910, 920 is approximately 1.73 times the area of theupper surface 930 under the pyramid 360. The light emission from thelight emission surfaces 910, 920 can assume a broad distribution 1280 asshown in FIG. 9.

An advantage associated with the disclosed light emission device andfabrication processes is that light emitting layers are constructed onsurfaces sloped relative to the substrate, which can significantlyincrease light emission areas and efficiency. Another advantage of thedisclosed light emission device and fabrication processes is thatsilicon wafers can be used to produce solid state LEDs. Manufacturingthroughput can be much improved since silicon wafer can be provided inmuch larger dimensions (e.g. 8 inch, 12 inch, or larger) compared to thesubstrates used in the conventional LED structures. Furthermore, thesilicon-based substrate can also allow driving and control circuit to befabricated in the substrate. The light emission device can thus be mademore integrated and compact than conventional LED devices. Anotheradvantage associated with the disclosed devices and fabricationprocesses is that the disclosed light emitting structures can befabricated using existing commercial semiconductor processing equipmentsuch as ALD and MOCVD systems. The disclosed fabrication processes canthus be more efficient in cost and time that some conventional LEDstructures that need customized fabrication equipments. The disclosedfabrication processes are also more suitable for high-volumesemiconductor lighting device manufacture. Yet another advantage of thedisclosed light emitting structures and fabrication processes is thatmultiple buffer layers can be formed to smoothly match the crystallattices of the silicon substrate and the lower group III-V nitridelayer. Yet another advantage of the disclosed light emitting structuresand fabrication processes is that a surface treatment is applied top-doped GaN to enhance light emitting efficiency. Yet another advantageof the disclosed LED structures and fabrication processes is that atransparent conductive layer formed on the light emitting layers and areflective layer formed under the light emitting layers can maximizelight emission intensity from the upper surfaces of the LED structures.Yet another advantage of the disclosed light emitting structures andfabrication processes is that light emitting layers are directly incontact with conductive metal substrate, which insures the best thermalconductivity during LED operation. This can increase both LED life timeand efficiency, especially for high brightness and high power LEDs. Yetanother advantage of the disclosed light emitting structures andfabrication processes is that there is a wafer level common electrode touse wireless wafer lever packaging.

The foregoing descriptions and drawings should be considered asillustrative only of the principles of the invention. The invention maybe configured in a variety of shapes and sizes and is not limited by thedimensions of the preferred embodiment. Numerous applications of thepresent invention will readily occur to those skilled in the art.Therefore, it is not desired to limit the invention to the specificexamples disclosed or the exact construction and operation shown anddescribed. Rather, all suitable modifications and equivalents may beresorted to, falling within the scope of the invention. For example, then-doped and the p-doped group III-V nitride layers can be switched inposition, that is, the p-doped group III-V nitride layer can bepositioned underneath the quantum-well layer and n-doped group III-Vnitride layer can be positioned on the quantum-well layer. The disclosedLED structure may be suitable for emitting green, blue, and emissions ofother colored lights. In another example, a (111) silicon wafer can beused as a substrate to allow trenches having (100) sloped surfaces toform in the substrate.

Moreover, the sloped protrusion surface can be at an angle between 20degrees and 80 degrees, or as a more specific example, between 50degrees and 60 degrees, relative to the upper surface of the substrate.The emission surfaces on a protrusion in the disclosed light emittingdevice can be more than 1.2, or 1.4, or 1.6 times of the base area ofthe protrusion. The large emission surface areas in the described lightemitting devices allow the disclosed light emitting device can thusgenerate much higher light emission intensity than conventional LEDdevices.

The disclosed systems and methods are compatible with a wide range ofapplications such as laser diodes, blue/UV LEDs, Hall-effect sensors,switches, UV detectors, micro electrical mechanical systems (MEMS), andRF power transistors. The disclosed devices may include additionalcomponents for various applications. A laser diode based on thedisclosed device can include reflective surfaces or mirror surfaces forproducing lasing light. For lighting applications, the disclosed systemmay include additional reflectors and diffusers.

1. A method of fabricating a light emitting device, comprising: forminga trench in a first surface on a first side of a substrate, wherein thetrench comprises a first sloped surface not parallel to the firstsurface, wherein the substrate has a second side opposite to the firstside of the substrate; forming light emission layers over the firsttrench surface, wherein the light emission layer is configured to emitlight; removing at least a portion of the substrate from the second sideof the substrate to expose at least one of the light emission layersforming a transparent conductive layer and over the exposed at least oneof the light emission layers.
 2. The method of claim 1, wherein thelight emission layers are configured to emit light in response to anelectric current flowing across the base electrode layer and thetransparent conductive layer.
 3. A method for fabricating a lightemitting device, comprising: forming light emission layers havingmonolithic crystal structures on a silicon substrate, wherein the lightemission layers are configured to emit light when an electric currentflows across the light emission layers, wherein the silicon substrate ison a first side of the light emission layers; forming a reflective layeron the second side of the light emission layers, the second side beingopposite to the first side; forming a base electrode layer on thereflective layer, wherein the base electrode layer comprises aconductive material; removing at least a portion of silicon substrate onthe first side of the light emission layers to expose at least one ofthe light emission layers; and forming a transparent conductive layerover the exposed at least one of the light emission layers.
 4. A methodfor making a light emission module, comprising: constructing one or morelight emitting structures on a conductive substrate, wherein each of theone or more light emitting structures comprises light emission layersand a transparent conductive layer on the light emission layers, whereinthe light emission layers are formed on one or more protrusions on theconductive substrate, wherein the one or more light emitting structuresfurther comprise an electrode layer around the protrusion, the electrodelayer in electric connection with the transparent conductive layer,wherein the electric interconnect is configured to electrically connectthe electrode layer to the second electrode; attaching the one or morelight emitting structures to amounting substrate by an electricinterconnect, the mounting substrate having a first electrode and asecond electrode; allowing the first electrode to be in electricalconnection with the conductive substrate; and allowing the secondelectrode to be in electric connection with the transparent conductivelayer, wherein the light emission layers in each of one or more lightemitting structures are configured to emit light when an electriccurrent flows across the first electrode and the second electrode. 5.The method of claim 4, wherein the electric interconnect includes awindow to allow light emitted from the light emission layers to passthrough when the one or more light emitting structures is clamped to themounting substrate by the electric interconnect.